This invention relates to tubing expansion, and in particular to expansion of tubing downhole.
The oil and gas exploration and production industry is making increasing use of expandable tubing, primarily for use as casing and liner, and also in straddles, and as a support for expandable sand screens. Various forms of expansion tools have been utilised, including expansion dies, cones and mandrels which are pushed or pulled through tubing by mechanical or hydraulic forces. However, these tools require application of significant force to achieve expansion and must be packed with grease to serve as a lubricant between the faces of the cone and the tubing. A number of the difficulties associated with expansion cones and mandrels may be avoided by use of rotary expansion tools, which feature rolling elements for rolling contact with the tubing to be expanded while the tool is rotated and advanced through the tubing; a range of such tools is disclosed in WO00 37766, the disclosure of which is incorporated herein by reference. Although the expansion mechanism utilised in rotary expansion tools tends to require only relatively low actuation forces, the various parts of the tools may experience high loading, for example the rollers may experience very high point loads where the roller surfaces contact the tubing under expansion. Clearly, such high loadings increase the rate of wear experienced by the tools and the requirement to build the tools with the ability to withstand such loads tends to increase the cost and complexity of the tools.
GB 2348223 A, GB 2347950 A and GB 2344606 A (Shell Internationale Research Maatschappij B. V.) disclose various arrangements in which a tubular member is extruded off a mandrel to expand the member. The axial force necessary to extrude and thus expand the member is achieved by creating an elevated fluid pressure chamber in the tubular member below the mandrel, which pressure creates an axial force on the closed end of the tubular member below the mandrel sufficient to pull the member over the mandrel. The elevated fluid pressure acts only the expanded portion of the tubular member below the mandrel.
U.S. Pat. No. 5,083,608 (Abdrakkhmanov et al) discloses an arrangement for patching off troublesome zones in a well. The arrangement includes profile pipes which are run into a borehole and then subject to elevated internal pressure to straighten the pipes and bring them into engagement with the surrounding wall of the borehole. A reamer is then rotated within the straightened pipes, with an axial load being applied to the reamer. The reamer is utilised to expand the threaded joints of the pipe and to further straighten the pipe, and also to provide clearance between a seal on the reamer and the inner wall of the pipe which was utilised to permit the original fluid pressure induced straightening of the pipe.
It is among the objectives of the present invention to provide an expansion method and apparatus which obviates or mitigates one or more disadvantages of the prior art expansion arrangements.
According to the present invention there is provided a method of plastically expanding a tubing, the method comprising:
Applying a fluid pressure expansion force to a section of tubing; and
Locating an expansion tool in the pressurised tubing and applying a mechanical expansion force to the pressurised tubing section, the combined fluid pressure force and mechanical expansion force being selected to be sufficient to induce yield of the tubing.
The invention also relates to apparatus for providing such expansion.
The use of a combination of fluid pressure and mechanical forces allows expansion to be achieved using a lower fluid pressure than would be necessary to achieve expansion when relying solely on fluid pressure to induce expansion, and furthermore provides far greater control of the expansion process; it is generally difficult to predict the form of the expanded tubing that will result from a solely fluid pressure-induced expansion, and failure of tubing in such circumstances is common. Also, the combination of fluid pressure and mechanically-induced expansion allows expansion to be achieved while the loads experienced by the mechanical expansion tool remain relatively low, greatly extending the life of the tools. By way of example, a tubing may be subject to an internal fluid pressure selected to induce a hoop tensile stress which represents 60% of yield. By then applying an additional mechanically-applied expansion force sufficient to induce yield, the tubing may be expanded. Of course the relative proportions of the stress contributed by the fluid pressure and by the expander tool may be varied to suit particular applications, and issues to be taken into account may include: the nature of the tubing to be expanded, as lower quality tubing may respond in an unpredictable manner to elevated hydraulic pressures, such that a greater proportion of the stress may be mechanically applied, and thus greater control exercised over the expansion process; and the capabilities of the apparatus available, for example pump or fluid conduit capabilities may place limits on the applied fluid pressures.
Various prior art proposals have utilised expansion dies or cones which are urged through tubing under the influence of an axial fluid pressure force acting on the die or cone, or in which tubing is extruded from a mandrel under the influence of axial fluid pressure force acting on the expanded tubing below the mandrel. However, in these instances the fluid pressure force is applied behind or below the die or cone, and the section of the tubing under expansion is not exposed to the elevated die-driving or tubing-extruding fluid pressure. Indeed, in order to provide the force necessary to drive the die or mandrel forward relative to the tubing in such existing arrangements, and to prevent leakage of the driving fluid past the die, it is necessary that there is an effective pressure-tight seal between the die and the expanded tubing. This seal may be provided by the contact between the die and the tubing wall, or by a separate seal assembly provided on the die.
It is a further advantage of the present invention that the fluid being utilised to pressurise the tubing may also serve as a lubricant between the expansion tool and the tubing, facilitating relative movement therebetween and thus reducing the degree of force necessary to move the expansion tool through the tubing. This is of particular significance where the expansion tool is a die or cone, and the section of the tubing under expansion is not exposed to he elevated die-driving or tubing-extruding fluid pressure. Indeed, in order to provide the force necessary to drive the die or mandrel forward relative to the tubing in such existing arrangements, and to prevent leakage of the driving fluid past the die, it is necessary that there is an effective pressure-tight seal between the die and the expanded tubing. This seal may be provided by the contact between the die and the tubing wall, or by a separate seal assembly provided on the die.
It is a further advantage of the present invention that the fluid being utilized to pressurise the tubing may also serve as a lubricant between the expansion tool and the tubing, facilitating relative movement therebetween and thus reducing the degree of force necessary to move the expansion tool through the tubing. This is of particular significance where the expansion tool is a die or cone, and the pressurizing fluid provides an effectively infinite supply of lubricant, as opposed to the finite supply of grease or other lubricant provided in conventional expansion arrangements, (see, for example, GB 2344606 A, in which a body of lubricant 275 is provided in the unexpanded portion of the tubing above the expansion mandrel); once the lubricant has been exhausted, the cone must be retrieved to the surface and repacked. Of course the presence of a lubricant will also reduce the rate of wear to the bearing portions of the expansion tool.
Although intended primarily for use in expanding bore lining metal tubing, the invention has application in other downhole applications, and may also be used in subsea or surface applications.
The expansion tool may take any appropriate form, including an expansion die or cone, and may be in the form of a cone or other member carrying a plurality of rollers rotatable about axes substantially perpendicular to the tubing axis. However, it is preferred that the expansion tool is a rotary expansion tool, or rolling element expander, that is the tool features at least one expansion member which, in use, is in rolling contact with the tubing wall; the expansion member may follow a circumferential or helical contact path with the tubing wall. Most preferably, the expansion members are conical in form or are mounted on axes arranged to define a cone. In another embodiment of the invention, a rotating expansion tool may be utilised which features a non-rotating expansion member or members, preferably of a relatively hard material such as a ceramic material, which provides a sliding contact with the tubing wall. The members may be radially extendable or may be radially fixed. In one embodiment, blocks of silicon carbide or titanium carbide may form the expansion members.
Preferably, the expansion tool is fluid pressure actuated, and may include a hydraulic drive motor to rotate the tool; the motor may utilise the fluid providing the expansion force as a drive fluid, the fluid exhausting into a lower pressure section of the bore isolated from the expansion section. In other embodiments, an electric motor may be utilised.
The expansion tool is preferably provided in combination with a seal assembly, for providing a fluid-tight seal with the unexpanded tubing ahead of the expansion tool. As the fluid pressure in the unexpanded tubing ahead of the seal assembly will tend to be lower than the elevated pressure behind the seal assembly, this differential pressure will tend to produce an axial pressure force acting on the seal assembly, which may be utilised to drive the expansion tool forwards.